In the area of CDMA (Code Division Multiple Access), particularly SFH-CDMA (Slow Frequency Hop-CDMA), it is important to compute an accurate estimate of the carrier-to-interference, or channel power ratio, for each hop. It is also important that the channel phase, induced due to multipath signals, be estimated accurately. Together, these two parameters, channel gain and phase, are referred to herein as channel response parameters.
Examples of measuring channel gain and phase are known in the art. However, these methods are typically computationally involved and result in relatively long delays in making the estimates.
Carrier phase recovery methods based on M-th power law devices and decision-feedback PLLs (Phase Locked Loops) are also known in the art. See Viterbi, Andrew & Viterbi, Audrey, Nonlinear Estimation of PSK-Modulated Carrier Phase with Application to Burst Digital Transmission, 29 IEEE Trans. on Information Theory 543-51 (July 1983) and Proakis, DIGITAL COMMUNICATIONS, 304-18 (2nd ed. 1989). However, use of these techniques in SFH-CDMA systems is hampered by the short hop duration which does not give the PLL or averaging schemes time to operate. In addition, these schemes operate under the assumption that the channel is an additive white Gaussian noise channel. In a synchronized SFH-CDMA system, this is an incorrect assumption since all of the symbols (desired and undesired) are synchronized. As a result, to a correlator receiver, the sum of interferers does not appear as white Gaussian noise.
Therefore, there exists a need in the art for a method of determining a channel response that is not subject to the above deficiencies.